Bohdan “Bep” Paczynski was born in Wilno, Poland (now Vilnius, Lithuania), and educated at Warsaw University, where he earned his Ph.D. in 1967. He worked at the Institute of Astronomy (since 1975 the Nickolas Copernicus Astronomical Center of the Polish Academy of Sciences) in Warsaw until 1982, when he moved to Princeton University, where he was the Lyman Spitzer Jr. Professor of Astrophysics. After observational studies of polarization and absorption in the Galaxy and of variable stars, he turned to theoretical work in stellar evolution and accretion disks around compact stars and in close binary systems. He wrote a widely-used stellar evolution code. He was known for theoretical work on gamma ray bursters, where he was an early proponent of the now-confirmed view that they are at cosmological distances. He proposed the use of gravitational microlensing as a technique for detecting compact objects in the galactic halo, and he was a leader of two major Polish-American sky surveys: the Optical Gravitational Lensing Experiment (OGLE) and the All-Sky Automated Survey, which is photometrically monitoring ten million stars.